1. Field of the Invention
The present invention relates generally to a dielectric ceramic composition suitable for use in a dielectric resonator, a filter, a multilayer capacitor or the like for high frequencies, and more particularly, to a non-reduction type dielectric ceramic composition sinterable at low temperatures which is high in Q value, has stable temperature characteristics, and can be sintered simultaneously with a material constituting inner electrodes such as silver or copper.
2. Description of the Prior Art
Inner electrodes in a dielectric resonator, a filter, a multilayer capacitor or the like used in a high frequency band must be constituted by a material which is low in resistance loss in the high frequency band. Consequently, the inner electrodes must be constituted by a metal material having high conductivity such as silver or copper. Further, as an effective way to miniaturize the above described electronic component, the electronic component is constructed as a monolithic type electronic component obtained by laminating ceramics while being separated by inner electrodes, followed by cofiring. In this case, however, it is required that dielectric ceramics sintered simultaneously with the above described material constituting inner electrodes is one which can be sintered simultaneously with the above described material constituting electrodes having a relatively low melting point, that is, can be sintered at temperatures of not more than 1000.degree. C. in addition to being high in Q value and low in temperature dependence of dielectric constant .epsilon.. In addition, when copper is used as the material constituting inner electrodes, it is required that the dielectric ceramics is a non-reduction type material so as to prevent the oxidation of the copper.
Japanese Patent Laid-Open Gazette No. 55815/1988 has proposed a dielectric ceramic composition of a BaO-SrO-SiO.sub.2 -ZrO.sub.2 -Al.sub.2 O.sub.3 system to meet the above described various requirements.
Furthermore, it has been known from Japanese Patent Laid-Open Gazette No. 131415/1987 that a particular additive component is added to a dielectric ceramic composition of a Ca(ZrTi)O.sub.3 system, so that the dielectric ceramic composition can be sintered at temperatures of not more than 1200.degree. C. and a high temperature coefficient and stable temperature characteristics can be achieved.
However, a material system disclosed in Japanese Patent Laid-Open Gazette No. 55815/1988 has the disadvantage in that the dielectric constant .epsilon. is 10, which is small, and the temperature coefficient of .epsilon. easily varies depending on the sintering conditions, that is, is unstable.
Furthermore, in a material system disclosed in Japanese Patent Laid-Open Gazette No. 131415/1987, the lower limit of the sintering temperature is 1030.degree. C., which is relatively high. Consequently, the material system has the disadvantage in that when copper is used as a material constituting inner electrodes, electrodes made of copper are melted and agglomerated and are diffused to a dielectric body, so that the absolute value of the temperature coefficient of .epsilon. becomes larger than 30 ppm/.degree.C.